1. Field
The disclosed concept pertains generally to rotating electrical apparatus and, more particularly, to systems for determining wellness of a rotating electrical apparatus, such as a motor. The disclosed concept also pertains to wellness circuits for rotating electrical apparatus. The disclosed concept further pertains to methods of determining wellness of a rotating electrical apparatus, such as a motor.
2. Background Information
Three-phase induction motors consume a large percentage of generated electricity capacity. Many applications for this “workhorse” of industry are fan and pump industrial applications. For example, in a typical integrated paper mill, low voltage and medium voltage motors may comprise nearly 70% of all driven electrical loads. Due to the prevalence of these motors in industry, it is paramount that the three-phase motor be reliable. Industry reliability surveys suggest that motor failures typically fall into one of four major categories. Specifically, motor faults typically result from bearing failure, stator turn faults, rotor bar failure, or other general faults/failures. Within these four categories: bearing, stator, and rotor failures account for approximately 85% of all motor failures.
It is believed that this percentage could be significantly reduced if the driven equipment were better aligned when installed, and remained aligned regardless of changes in operating conditions. However, motors are often coupled to misaligned pump loads or loads with rotational unbalance and fail prematurely due to stresses imparted upon the motor bearings. Furthermore, manually detecting such fault causing conditions is difficult at best because doing so requires the motor to be running. As such, an operator is usually required to remove the motor from operation to perform a maintenance review and diagnosis. However, removing the motor from service is undesirable in many applications because motor down-time can be extremely costly.
As such, some detection devices have been designed that generate feedback regarding an operating motor. The feedback is then reviewed by an operator to determine the operating conditions of the motor. However, most systems that monitor operating motors merely provide feedback of faults that have likely already damaged the motor. As such, although operational feedback is sent to the operator, it is usually too late for preventive action to be taken.
Some systems have attempted to provide an operator with early fault warning feedback. For example, vibration monitoring has been utilized to provide some early misalignment or unbalance-based faults. However, when a mechanical resonance occurs, machine vibrations are amplified. Due to this amplification, false positives indicating severe mechanical asymmetry are possible. Furthermore, vibration based monitoring systems typically require highly invasive and specialized monitoring systems to be deployed within the motor system.
In light of the drawbacks of vibration based monitoring, current-based monitoring techniques have been developed to provide a relatively more inexpensive, non-intrusive technique for detecting bearing faults.
It is known to employ motor current signature analysis to detect various motor faults. See, for example, U.S. Pat. No. 5,629,870.
Known products employing motor current signature analysis technology have a definite purpose (i.e., motor wellness) and a relatively high cost as compared to typical motor protection devices, such as electronic overloads.
U.S. Patent Application Publication No. 2009/0146599 discloses the detection of abnormal conditions to predictively determine potential motor faults. Current signature analysis (CSA) is utilized to review raw data received from a plurality of sensors of a controller monitoring an operating motor. The system, which is preferably disposed within the controller, decomposes the sensed/monitored current into a non-fault component and a fault component, and performs a noise-cancellation operation to isolate the fault component of the current and generate a fault identifier. An operator of the monitored motor system is then proactively alerted of a potential fault prior to a fault occurrence. A notch filter, a low pass filter and an analog-to-digital (A/D) convertor operate to receive raw data generated by current sensors and prepare the raw data for processing by a processor. The filters are used to eliminate the fundamental frequency (e.g., 60 Hz in US and 50 Hz in Asia) and low frequency harmonics, as these harmonic contents are not related to bearing failure. Removing such frequencies (especially the base frequency component) from the measured current data can greatly improve the A/D conversion resolution and signal-to-noise ratio (SNR), as the 60 Hz frequency has a large magnitude in the frequency spectrum of the current signal.
It is known to employ a high-pass filter, a band-pass filter, or a notch filter prior to demodulation to increase sensitivity to motor frequency components and decrease sensitivity to mechanical components (e.g., gear meshing; belt turning).
It is believed that no existing product or solution provides a cost effective and well defined way to add a motor wellness function to a base product, such as, for example, a three-phase switching, control, protection or monitoring device.
There is room for improvement in systems for determining wellness of a rotating electrical apparatus, such as a motor.
There is also room for improvement in methods of determining wellness of a rotating electrical apparatus, such as a motor.